Nonreciprocal Enhancement of Optomechanical Entanglement Based on Sagnac Effect and Pump Modulation

A scheme is proposed to enhance the optomechanical entanglement nonreciprocally in a spinning cavity optomechanical system driven by a periodically modulated pump field. Based on the Sagnac effect induced by the resonator's spinning, the direction-dependent frequency shifts are introduced to the counterpropagating optical modes. By combining the Sagnac effect with periodic pump modulation, the optomechanical entanglement can be enhanced nonreciprocally by a factor of about 1.67. It is shown that the negative effect of the backscattering losses on nonreciprocal entanglement enhancement can be eliminated by spinning the resonator. Meanwhile, the enhanced entanglement exhibits strong robustness against thermal noise, surviving even at environmental temperature up to 0.99 K. This work is expected to promote the development of nonreciprocal quantum networks and quantum control techniques.